<template>
  <div class="progress-bar" ref="progressBar" @click="progressClick">
    <div class="bar-inner">
			<!-- 黄色走过的区域 -->
      <div class="progress" ref="progress"></div>
			<!-- 按钮 -->
      <div class="progress-btn-wrapper" ref="progressBtn"
           @touchstart.prevent="progressTouchStart"
           @touchmove.prevent="progressTouchMove"
           @touchend="progressTouchEnd"
      >
        <div class="progress-btn"></div>
      </div>
    </div>
  </div>
</template>

<script >
  import {prefixStyle} from 'common/js/dom'

  const progressBtnWidth = 16
  const transform = prefixStyle('transform')

  export default {
    props: {
      percent: {
        type: Number,
        default: 0
      }
    },
    created() {
      this.touch = {}
    },
    methods: {
			// 小球手指3事件
      progressTouchStart(e) {
        this.touch.initiated = true
        this.touch.startX = e.touches[0].pageX
        this.touch.left = this.$refs.progress.clientWidth
      },
      progressTouchMove(e) {
        if (!this.touch.initiated) {
          return
        }
				//手指纵向是我偏移量
        const deltaX = e.touches[0].pageX - this.touch.startX
        //手指可能大于总长度 要加以限制
				const offsetWidth = Math.min(this.$refs.progressBar.clientWidth - progressBtnWidth, Math.max(0, this.touch.left + deltaX))
        this._offset(offsetWidth)
      },
      progressTouchEnd() {
        this.touch.initiated = false
				//结束派发事件
        this._triggerPercent()
      },
			//获取小球偏移量
      progressClick(e) {
        const rect = this.$refs.progressBar.getBoundingClientRect()
        const offsetWidth = e.pageX - rect.left
        this._offset(offsetWidth)
        // 这里当我们点击 progressBtn 的时候，e.offsetX 获取不对
        // this._offset(e.offsetX)
        this._triggerPercent()
      },
      _triggerPercent() { //实时更新时间
        const barWidth = this.$refs.progressBar.clientWidth - progressBtnWidth
        const percent = this.$refs.progress.clientWidth / barWidth
        this.$emit('percentChange', percent)
      },
      _offset(offsetWidth) {
				// 黄色的进度条  小球的偏移
        this.$refs.progress.style.width = `${offsetWidth}px`
        this.$refs.progressBtn.style[transform] = `translate3d(${offsetWidth}px,0,0)`
      }
    },
    watch: { //监听滚动条的变化
      percent(newPercent) {
        if (newPercent >= 0 && !this.touch.initiated) {
					// 滚动条减去-小圆球的宽度
          const barWidth = this.$refs.progressBar.clientWidth - progressBtnWidth
          const offsetWidth = newPercent * barWidth
          this._offset(offsetWidth)
        }
      }
    }
  }
</script>

<style lang="less"  scoped>
	   @import '../../common/stylus/variable.less';

  .progress-bar{
    height: 30px;
    .bar-inner{
      position: relative;
      top: 13px;
      height: 4px;
      background: rgba(0, 0, 0, 0.3);
      .progress{
        position: absolute;
        height: 100%;
        background: @color-theme;
			}
      .progress-btn-wrapper{
        position: absolute;
        left: -8px;
        top: -13px;
        width: 30px;
        height: 30px;
        .progress-btn{
          position: relative;
          top: 7px;
          left: 7px;
          box-sizing: border-box;
          width: 16px;
          height: 16px;
          border: 3px solid @color-text;
          border-radius: 50%;
          background: @color-theme;
					}
					
					
				}
			}
		}
		
</style>